Belief in three gods which denies the unity of substance in the Christian doctrine of the Trinity. Popular expressions of Trinitarian doctrine and some transactional soteriological theories can be tritheistic. Historical tritheism appeared in Monophysite circles c.550, associated with Johannes Askunages and Johannes Philiponus. Philoponus was an Alexandrian philosopher who opposed the Chalcedonian Christology, contending that Christ's was a single nature compounded of the divine and human, and that there are three divine substances (ousiai) in the Trinity. A speculative rather than a practical tritheism, it was opposed by John of Damascus in de Fide orthodoxa.

In medieval times the extreme Nominalism* of Roscellinus* of Compiègne and the exaggerated Realism of Gilbert de la Porrée led them into tritheistic positions which were condemned at the Councils of Soissons (1092) and Reims (1148) respectively. Gilbert's teaching influenced Joachim of Fiore,* who conceived the oneness of the three persons as a mere generic unity. Joachim's doctrine was condemned at the Fourth Lateran Council (1215), which defined clearly the numerical unity of the divine nature.

Anton Günther (1783-1863), opposing Hegelian pantheism, taught that the Absolute determined itself three times in a process of self-development. The divine substance is trebled, and the three substances attracted to one another through consciousness make a formal unity. This was condemned by Pius IX (1857).